Foods that boost metabolism

The claim, as heard: "Green tea, chilli, coffee — they boost your metabolism and burn fat while you sit."

What the data show. Some of these do something measurable. A meta-analysis of short laboratory studies finds that catechin-rich tea and caffeine raise energy expenditure and fat oxidation over the following hours — by an amount that, scaled to a day, comes to tens of kilocalories, perhaps a hundred at the upper end with high doses. The same review is careful about the rest: the studies are short and controlled, the effect on body weight in longer trials is small or absent, and supplements are not recommended. Tens of kilocalories is the energy in a bite of bread; it is real, and it does not show up on a scale.

Verdict: for the sale — "burns fat", "boosts metabolism" — the claim fails; for the mechanism, there is a small, short-lived effect that the evidence supports. Evidence grade B for the mechanism, from a meta-analysis of short studies; no evidence of a meaningful weight outcome.

The grain of truth. Caffeine and catechins do raise expenditure a little for a few hours. Chilli's compound does something similar, smaller still. Nothing here is fictional; it is just tiny.

One sentence to remember: a "metabolism-boosting" food changes your day by less than the cup it came in; the deficit still has to come from what you eat.

The daily energy step shows what actually moves expenditure — body size, activity and the ordinary day — and by how much.